TvSubst, TvSubstEnv, mkTvSubst, setTvSubstEnv, substTy,
extendTvSubst, composeTvSubst, substTyVarBndr, isInScope,
getTvSubstEnv, getTvInScope, mkTyVarTy )
TvSubst, TvSubstEnv, mkTvSubst, setTvSubstEnv, substTy,
extendTvSubst, composeTvSubst, substTyVarBndr, isInScope,
getTvSubstEnv, getTvInScope, mkTyVarTy )